Circular polarizers are a special case of elliptical polarizers. Circular polarizers convert a linearly polarized electromagnetic wave into a circularly polarized wave, or a circularly polarized wave into a linearly polarized wave.
In the case where a circularly polarized wave is to be converted into a linearly polarized wave, it is generally the case that two linearly polarized waves which are orthogonal to each other constitute the circularly polarized wave and the phases of the two linearly polarized waves are displaced by 90 degrees. A circularly polarized wave Ec is converted into a linearly polarized wave Er by retarding the phase of the linearly polarized wave that is advanced 90 degrees to set the phase difference, to 0 degrees.
Conventional circular polarizers are commonly embodied as quarter-wave plates. As such, a common feature of conventional circular polarizers is the need for large, bulky optical components, and/or the requirement for a large resonant cavity for polarization conditioning. Conventional circular polarizers are also generally formed using costly materials.
As known in the art, the modification of the spectral radiation signature of a surface, in absorption, reflection, or transmission, is possible by patterning the surface with a periodic array of electrically conducting elements, or with a periodic array of apertures in an electrically conducting sheet. Spectral modifications have been disclosed using such structures for millimeter-wave and infrared radiation applications and are known as frequency selective surfaces (FSS). As known in the art, in order for its structure to affect electromagnetic waves, the FSS must have structural features at least as small, and generally significantly smaller, as compared to the wavelength of the electromagnetic radiation it interacts with.
Such surfaces have been configured to function as spectral filters, such as low-pass, high-pass, bandpass, or dichroic filters. FSS can even be used as narrowband infrared sources, by virtue of Kirchhoff's Law in which the FSS absorptive properties equal its emissive properties. Other applications include FSS use as a pollutant sensing element, as a reflecting element in an infrared laser cavity and as an infrared source with a unique emission spectrum.
Certain applications could benefit from new FSS-based polarization filters. Moreover, some new applications and related systems could arise from such filters.